The present invention relates to a process for the manufacture of cooking vessels, and also a vessel as above defined, obtained according to such process.
In particular, the invention relates to cooking vessels, e.g., of the type shaped starting from a flat member in a relatively soft metallic material, e.g., made of aluminium, and comprising a bottom portion reinforced with said plate member which is formed in a metallic material of relatively high hardness, e.g., steel-based, anyhow having properties making it heatable with a magnetically induced current.
Of course, it has to be understood that the present invention further relates to different cooking vessels, like, e.g., those formed by die-casting or extrusion.
The type of vessel generally comprises pots and pans, also comprising different vessels, like coffee makers, kettles, grill plates etc.
The processes and the related vessels of the above specified type are known in the art. For instance, the French Patent Application No. 91 03695 and the European Patent No. 0,604,617, in the name of SEB S. A., describe a step in which the plate member and the flat member are reciprocally connected with a hot press-stamping.
In this step, the soft material of the flat member is heated and softened. Then, the plate member, that is provided with holes and/or fissures, is press-stamped, e.g. with a hammer or the like, in such a way that the steel plate member is embedded into the aluminium flat member while the latter, due to the induced pressure, penetrates inside said holes.
Such process is disadvantageous due to several reasons, among which the necessity of a step of heating the aluminium, with the entailed consumption of energy and time, and the need to protect the aluminium itself from oxidation processes.
In the European Patent No 0,509,860, a method is described for embedding a holed steel plate in an aluminium layer apt to be manufactured in order to obtain a cooking vessel. According to such method, the embedding is carried out with an energetic step of cold press-stamping, in which the malleability of the aluminium is exploited that is forced to penetrate inside the holes and the fissures of the plate to the level of the outer surface of the holed plate.
Such step, preceding the drawing of the aluminium layer, is a remarkable trauma for the materials, it requires the use of high pressures for the cold press-stamping, and implies the subsequent manufacturing steps to be carried out with an already applied plate.
Moreover, these two embodiments could entail problems due to the different thermal expansion of the materials used.
In the Swiss Patent No. 227,769 a further method is described for coupling, wherein a spiral-shaped reinforcing member is irreversibly forced inside a groove, of similar shape, formed on a face of the flat member in a soft material.
This method, besides entailing an additional step of hot- or cold forming of said groove, does not allow an application of a real plate member.
In the Italian Patent Application No. RM91A000355 a further method is described, according to which a metallic plate of ferritic steel is fixed to the bottom of a pot by forcing and crimping the edge of the plate inside a peripheral groove surrounding the bottom of the pot already shaped.
This method, although performing an effective coupling without overly traumatising the material, does not provide a suitable reinforcement.
In light of the above described known art, the invention aims at attaining the object of manufacturing a cooking vessel provided with a plate bottom for heating of the magnetic induction type that can be manufactured in an easy and effective way.
The technical problem underlying the present invention is that of providing a process for the manufacture of cooking vessels allowing to overcome the drawbacks mentioned with reference to the prior art.
Such problem is solved by a process as above specified, characterised in that it comprises the following steps:
providing a metallic semimanufactured vessel of the cooking vessel, comprising a hollow and a bottom portion;
providing a plate member, in a metallic material of relatively high hardness, provided with a plurality of points projecting from a surface thereof and forming a angle greater than or equal to 90xc2x0 therewith;
inducing, by compression of the plate member at the bottom portion, the penetration of said points and the adhering of said surface of said plate member on said bottom portion.
The present invention further relates to a cooking vessel obtained according to the process as above defined, further comprising deposition steps of one or more non-stick layers as well as finishing steps of the vessel.
The main advantage of the process for the manufacture according to the present invention lies in allowing an effective securing of the plate member without traumatising the materials and with no further specific steps required.
Moreover, the manufacture of the cooking vessels can follow a normal manufacture process, comprising press-stamping and coining steps needed to secure the plate member, while the latter step can be carried out in parallel, yet in a substantially autonomous way.
Furthermore, with the above described process it is possible to secure a plate member regardless of the latter extension with respect to those of the bottom portion at issue.
Further, a vessel bearing a plate member coated with a layer of possibly non-stick coating can also be manufactured, without entailing additional manufacturing steps or a different arrangement of the work stations commonly used in the manufacture of cooking vessels.